Jeffreys Bay Pro 2015

[chrisb]

Corner Inlet/Lakes Entrance. No, just the one I reckon. They are talking about an approximately 200 kms stretch.
I guess it indicates just how far they normally do roam when 200 kms is considered staying local for a while.

Yeah, your'e right. The two places are much closer than I thought, just 170kms, both part of Gippsland. It always looked a bit sharky on the few occasions that I visited those places.

[Davros]

Juve GWS love Salmon. If I'm in the Newcastle - Port Macquarie area and see them or fisherman coming back with buck loads I tend to not go out. They pop up in numbers at the long reef to DY stretch, a few people recently have been chased out of the water by they think a Bronze Whaler or Mako feeding up near Poles. I hear about a GWS hanging off Long Reef from time to time, Bomborraa post makes sense after the past sightings. Fisherman said to me once don't worry about the Bronzey they are generally s bit flighty and would be curious and a little worried, he went on to say pray it's not a Bull Shark out there because they are complete pricks.

[bomboraa]

Actually southern bluefin in Australia are on the up and up. Thanks to the Japs being busted quite a while ago illegally over fishing the crap out of them south of Southern Australia, and some pretty strict catch limits in Oz. They now turn up off Sydney, and the entire southern NSW coast, in winter. This hasn't happened since the 70s. They don't go much further north than Newcastle on their winter east coast run. Mate has taken SBTs to 100kg off Sydney last several winters and has videos of massive schools of school fish around 30kgs. There's a heap of Sydney big boats, and not so big trailer boats, out fishing em today thanks to the calm conditions. Yellowfin tuna on the east coast on the other hand are a poor shadow of the past.
Stacks of SBTs off Vic and SA too. In NSW they are generally super wide: from the shelf to as far as you wanna travel. In SA and southern Vic they can be found quite close to shore.

[bomboraa]

Juve GWS love Salmon. If I'm in the Newcastle - Port Macquarie area and see them or fisherman coming back with buck loads I tend to not go out. They pop up in numbers at the long reef to DY stretch, a few people recently have been chased out of the water by they think a Bronze Whaler or Mako feeding up near Poles. I hear about a GWS hanging off Long Reef from time to time, Bomborraa post makes sense after the past sightings. Fisherman said to me once don't worry about the Bronzey they are generally s bit flighty and would be curious and a little worried, he went on to say pray it's not a Bull Shark out there because they are complete pricks.

Remember the lifeguard having a lunch break surf just south of poles a few December's ago: board got bit while up and riding by a 2.5m white? The bugger refused to leave when buzzed by rescue chopper, and came back the next day to exact same part of beach and, again, wouldn't budge while being buzzed by chopper. Measurement came from checking the bite mark on his board. Salmon love hanging in any holes in that area.

[alakaboo]

Bomboraa probably has a better idea, braithy, but I think the idea that big whites only eat mammals is overblown. Probably because it has a longer residence time in the digestive tract.
I know for a fact that they eat stingrays.

A big meal would keep them going for a while. With the water this warm most of their energetic needs are met, and they are very efficient swimmers.

Plus, dolphins.

[crabmeat thompson]

yeah for some reason, i thought yellowfin were the tuna whites went after. i never gave much thought to the blues.

good to know they're on the climb population wise.

[crabmeat thompson]

Bomboraa probably has a better idea, braithy, but I think the idea that big whites only eat mammals is overblown. Probably because it has a longer residence time in the digestive tract.
I know for a fact that they eat stingrays.

A big meal would keep them going for a while. With the water this warm most of their energetic needs are met, and they are very efficient swimmers.

Plus, dolphins.

so fishing stock numbers – salmons, blues etc – could be a direct correlation to whites being inshore more?

[alakaboo]

I also think pretty much all of the sizes being reported are bullshit too. I've done some research on perception of distance and without a reference like a boat or a ski people tend to be out by about 50% and with sharks it's always over.

Dunno braithy. Without doing a lot more research I'd just be guessing. I reckon there'd be a direct correlation between wetsuit sales and shark attacks but it still wouldn't explain anything.

[alakaboo]

Although for most species the fatality rate drops off with age, so more food for juveniles would lead to more surviving to adulthood, where not much troubles them.

[crabmeat thompson]

Dunno braithy. Without doing a lot more research I'd just be guessing.

but you're guessing is still a really bloody educated form of guessing with more insight than i could ever conjure.

[MrMik]

Today I have been testing and comparing the SurfSafe and SharkShield Freedom7 for effectiveness against attack by a GWS.

Here is a picture of the GWS, a SharkShield Freedom7, a SurfSafe mounted to a piece of timber, and a near irresistible bait:


The GWS is fairly tame, but not very well trained. Therefore, there is not too much chance of influencing his behaviour in the presence of the bait ball. The lack of effective training is thought to limit the ill effects stemming from the total lack of blinding in the following experiments

The GWS can appear relaxed and graceful, but in stalking or attack mode the prey will rarely see him before it is too late:



The SurfSafe has been slightly modified, just so that it can be used without a surfboard surrounding it.
The modifications involve:
a) sealing of the back of the SurfSafe (where the electrode cable is attached to the main housing with a nut) with Zerovoc epoxy resin against water contact. This is done so that the nut and the end of the cable do not act as an additional electrode.
b) sealing of the back of the electrode at the end of the cable with epoxy resin, so that only the screw head is exposed to the water.
c) attaching the SurfSafe to a thin piece of timber with cable ties, and wrapping it up in some yum-yum-yellow tape, for added protection in case of some exploratory bites. The electrodes are thus fixed 900mm apart.
In other words, electrically the SurfSafe should behave exactly as if it was installed according to instructions into a surf board.

The SharkShield Freedom7 is completely unmodified.


http://surfsafe.net.au/
https://www.sharkshield.com/
http://solarez.com/products/zerovoc-epoxy-resin/

[MrMik]

The results of the various tests I have done to compare the SurfSafe and the SharkShield Freedom7 are all completely consistent and conclusive:

The SharkShield Freedom7 delivers much more powerful electric impulses into the water than the SurfSafe.

But first, some experiments performed on a dry dining table:

I measured the voltage drop across a 0.22 ohm (5W) resistor with each device.

With the SharkShield Freedom7, the ceramic resistor gets quite hot, but with the SurfSafe it stays pretty cool.

The oscilloscope shows that the SurfSafe delivers current across the 0.22ohm resistor with a voltage drop of 30V and a duration of about 100us:


The SharkShield Freedom7 delivers pulses of 300us duration with a peak voltage drop across the 0.22 ohm resistor of about 55V:


The pulses are much more frequent with the SurfSafe than with the SharkShield Freedom7:
SurfSafe: About 15 pulses/second.
SharkShield Freedom7: 1.66 pulses/second.

A current causing a 55V drop across 0.22 ohm should be (V/R = I) 55v/0.22ohm= 250A. That is more than the advertised 150A, and I think it is therefore reasonable to assume that the SharkShield pulses actually reach the advertised 150A peak, and that the resistance in the circuit which I clamped together is 55v/150A= 0.366 ohm. The actual resistance is higher than the specified 0.22ohm because the contact against the stainless steel braid is less than perfect.

Assuming that the resistance due to poor contact is the same in the circuit for the SurfSafe, then the SurfSafe pulses peak at 30v/0.366ohm = 81.96A

The peak power output into the resistor (or the salt water) is:
SharkShield Freedom7: 150A x 150A x 0.366 ohm = 8235W = 8.24kW
SurfSafe : 81.96A x 81.96A x 0.366ohm = 2458.58W = 2.46kW

Seems like a lot of power, but the pulses are so short that the average power is not all that much:
For the SharkShield: 0.3ms on, then 599.7ms off, and rapidly falling power during the 0.3ms long 'on' period results in an average power of (0.3ms / 599.7ms) x 8235W x 0.3 = 1.235W average.
For the SurfSafe: 0.1ms on, then (1000/15=) 66.66ms off, x 0.3 for the rapid fall of power during the 'on' period, makes an average of: (0.1ms/66.66ms) x 2458.58W x 0.3 = 1.106W average.

I don't understand why the resistor gets hot with the SharkShield but not with the SurfSafe, when their average energy output over time is so similar, but it explains why their battery life (claimed, not tested) is not vastly different.

The oscilloscope-measured difference in peak energy output corresponds well with my subjective experience and with the subjective experience of the ad-hoc ethics committee. We tested this by putting hands and feet near to the devices when submerged in salt water.

Before exposing the German White Shepherd to the electronic devices in salt water, the entire ethics committee subjected themselves to the same treatment and found it harmless enough.
The SharkShield feels much like touching a cattle fence with a wet grass blade, and the SurfSafe more like gently turning on a TENSE machine as you gradually get closer.
With a bit of time I got so used to it that I managed to hold my hand directly next to the SharkShield electrodes, and could even firmly touch the plastic mesh surrounding the braided SS electrode. It does not hurt, it's just a bit scary when you don't know what to expect.
In a salt water puddle, the pulses from the SharkShield can be clearly felt from at least half a metre away, but you need to put your hand to within 10cm of the SurfSafe electrodes to feel the (much faster) pulsations.

When we got to the beach, we found that someone had already dug up a set of great little laboratory pools for us:

[MrMik]

Now to the beach tests of the SurfSafe and SharkShield Freedom7 devices:


The GWS = German White Shepherd put one foot into the larger pool with the SharkShield Freedom7 device and then refused to step into it again. I did not record that first step in and it was quite unspectacular.

The GWS then proceeded to walk into the smaller pool with the SurfSafe in it, stood in it quite relaxed and then lay down. (He likes to do that and I think this had been his initial plan for the larger pool, too). He lay there in the water for a couple of seconds, then stood up and stepped on the distal electrode of the SurfSafe, whereupon he became airborne and disappeared much like Wiley Coyote.......:


Nevertheless, he was quite prepared to repeatedly get the ball back out of the pool with the SurfSafe. Note how close the ball in the picture below was to the distal electrode. This ball sinks to the bottom:



Not so with the pool that had the SharkShield in it. This is the closest that the GWS dared to go near the SharkShield after putting one foot in, only once. He stands at the edge of the pool, without stepping into the water, and carefully sniffs at the Shar Shield. The ball can be seen lying in the shady part of the pool.


The link below leads to a video showing how the GWS refuses to get the bait from near the SharkShield Freedom7, and then immediately gets it out of the pool with the SurfSafe:
http://vid281.photobucket.com/albums/kk ... fe_GWS.mp4


The next video link shows how the GWS gets the bait without hesitation from the SurfSafe pool:
http://vid281.photobucket.com/albums/kk ... fe_GWS.mp4


And the last video shows that the GWS had associated the shocks more with the pool than with the device in it. I swapped the SurfSafe and the SharkShield Freedom7 into opposite pools towards the end, and the GWS tried to get the bait out from the SharkShield pool, but could not put his mouth near the bait. Note how far the bait is from the SharkShield electrodes:
http://vid281.photobucket.com/albums/kk ... ld_GWS.mp4

[Beerfan]

I want the 4 seconds it took to scroll past all that garbage back

[crabmeat thompson]

I read it all too. I'm not sure either would do much of anything with a white around.

Wasn't one of the divers who got taken in WA wearing a shark shield?

[MrMik]

I want the 4 seconds it took to scroll past all that garbage back

Some are just slower scrollers than others, maybe you need the exercise?

There's another second gone, gotcha!

[Cranked]

Wasn't one of the divers who got taken in WA wearing a shark shield?

Im not aware of that in WA but there was that diver killed while doing research in SA while wearing one.

[crabmeat thompson]

Yeah, that's the one